Sustained drug release from nanoparticles can improve mucosal therapies by reducing systemic side-effects, and sustained topical vaginal delivery is likely to greatly improve protective efficacy, and user-acceptability, of microbicides now being developed for protection against AIDS and other sexually transmitted diseases. Nanoparticles now used for mucosal drug delivery are mucophilic and bind tightly to mucus gels. Unfortunately, these conventional nanoparticles are rapidly cleared with luminal mucus and very few reach the epithelial surface;luminal mucus is cleared within minutes to hours. Our first hypothesis is that non-mucophilic particles that rapidly penetrate mucus will provide longer, and more efficient, sustained delivery, by diffusing through luminal mucus to reach the unstirred layer of mucus that adheres to the epithelium. Our second hypothesis is that mucus-penetrating particles decorated with cell-adhesion molecules will reach and bind to epithelial cells with high efficiency, and will persist in place until the epithelial cells are shed, a much slower process than clearance of mucus secretions. Viruses evolved mechanisms to penetrate mucus secretions and bind to target epithelial cells, and, using virus particles as guides, we have recently developed nanoparticles that can rapidly diffuse through human mucus secretions and bind tightly to epithelial cells. We will test in mice whether our mucus-penetrating, and cell-adherent, particles are retained more efficiently and for longer times in the vagina than conventional mucophilic nanoparticles. In Aim 1, we will fully characterize particle size and surface properties, and use particle tracking to observe diffusional transport rates of mucus-penetrating and conventional nanoparticles in undiluted human cervico-vaginal mucus. In Aim 2, we will determine in mice the retention times and vaginal distributions of the nanoparticles characterized in Aim 1. The particles will be fluorescently labeled, and details of epithelial distribution will be examined with histologic methods. Vaginal retention times will be quantified in living animals using whole-body fluorescence imaging. In Aim 3, we will synthesize mucus-penetrating, cell-adherent particles using a new biodegradable polymer platform. We expect conventional mucophilic particles will be cleared within hours, but mucus-penetrating, and especially cell-adherent mucus-penetrating particles, will achieve complete epithelial coverage and be retained for days. Public Health Relevance: Vaginal microbicides now being developed to prevent AIDS and other sexually transmitted diseases, and drug therapies for many types of vaginal infections are likely to be greatly enhanced if methods can be developed for sustained vaginal delivery. Topical applications of drugs typically reduces most types of side effects, but topical applications typically have relatively short durations of action or protection: Vaginal spermicidal are effective for only about 1 hour. Recently we discovered ways to produce mucus-penetrating nanoparticles that are likely to provide an efficient method for sustained topical delivery of drugs and microbicides to the vaginal epithelium. This application seeks funds to test in animals the hypothesis that mucus-penetrating nanoparticles will be retained within the vagina for significantly longer times than conventional drug-delivery nanoparticles since conventional nanoparticles adhere strongly to mucus and hence are cleared as rapidly as the mucus is shed (typically minutes to hours). In addition, it appears possible to develop mucus-penetrating particles than can diffuse to, and bind to, the epithelial cells that line the vagina. Such particles are likely to provide sustained topical drug delivery for several days. If successful, this project could lead to the development of sustained drug delivery systems that are more convenient, and more effective, for preventing and treating diseases than methods now available.